On Wed, 8 Sep 2010 08:01:55 +1000 Neil Brown <neilb@xxxxxxx> wrote: > On 7 Sep 2010 10:19:04 -0400 "George Spelvin" <linux@xxxxxxxxxxx> wrote: > > > > I'm worried that someone not paying attention will --add rather than > > --re-add the off-site backup drives and create mirrors 4 and 5 of > > the first stripe half, thus producing an incomplete backup. > > It is already on my to-do list for mdadm-3.2 to reject a --add that looks > like it should be a --re-add. You will need --force to make it a spare, or > --zero it first. > I just realised I had this slightly wrong. mdadm will already perform a --re-add if asked to --add a device that can be re-added. So you should be safe from people accidentally using --add when they should have used --re-add. The change on my to-do list is that if it looks like a re-add might be possible but the re-add fails, then don't do a normal --add without extra encouragement. The case where this is interesting is if you have a doubly-degraded RAID5 and the devices just had a temporary failure. It would seem logical to just add the disks back. The --re-add attempt will fail of course, so mdadm will currently make the devices spares which isn't what is wanted. Rather mdadm should fail and suggest a 'stop' followed by '--assemble --force'. For raid1 my planned change won't make any difference - you should be safe as you are. NeilBrown > > > > > Any suggestions on how to mitigate this risk? And if it happens, > > how do I recover? Is there a way to force a drive to be added > > as 9/10, even if 5/10 is currently empty? > > 1/ hack at mdadm or wait for mdadm-3.2, or feed people more coffee:-) > 2/ You probably cannot recover with any amount of certainty. > 3/ That is entirely a kernel decision - 'fix' the kernel. > > NeilBrown > > > > > > > > Thank you very much! > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
